The manga will be a more traditional Arthurian tale
The manga will be a more traditional adaptation of
Arthurian Legend, showcasing: the Round Table Knights (Gawain, Percival, etc), Tristan's lover Isolde, Lancelot's son Galahad (who is Ban's grandson), Morgan Le Fay and her son Mordred and the Holy Grail.
Tristan's demonic powers relate to spreading disease.
1) He's presumably titled "Knight of Pestilence" for a reason, 2) it's suspicious how his angelic powers specifically can't heal disease, and 3) his nephilim heritage probably means he'll have dual powers that oppose each other in some way.
Nasiens is female.
Fairly obvious, but put here for posterity. "He" looks ambiguously-gendered (being short and slender) in a setting where that isn't the norm, refuses to go to the bathroom with the other males in the party, and is said by Anne to be keeping one constant secret, long after his backstory and motivations have been revealed to the characters. Furthermore, despite the
Clothing Damage that everyone suffers with all the magic flying around, we have
never, over multiple volumes of story, seen any part of Nasiens' body that shows his gender. This is likely a deliberate choice on the mangaka's part to lay ground for
The Reveal.
Arthur will marry Guinevere, but she will cheat on him with Lancelot.
It should come to no surprise, given their namesakes.
A lot of the characters in this series are inspired by characters in the Arthurian Legend, so Arthur and Guinevere will get married but she will cheat on Arthur with Lancelot AFTER the manga gets a Time Skip. Look at Meliodas/Elizabeth and Ban/Elaine for example, both pairings are based off couples from the Arthurian Legend. Keep in mind when Guinevere met Lancelot, she proclaimed that she will become his lover in the future, not his wife. She can see into the future so maybe she also saw her future marriage to Arthur, or maybe she hasn’t yet, which explains why she was so excited to meet her future boyfriend. Lancelot did see her older self as a bride, in a mountain where you can see who your future lover will be.
